A liquid crystal display device is a flat panel display that is now most widely used. Particularly, an active matrix liquid crystal display device including a TFT (thin film transistor) is now being used in consumer equipments such as a personal computer, a word processor, and a cellular phone, and its market is expected to be further expanded. With expansion of the market, further improvement in image quality is needed for such a liquid crystal display device.
With regard to the active matrix liquid crystal display device, a technology of forming a storage capacitor element in a pixel region in order to maintain a voltage applied to a liquid crystal layer for a certain period is known. In a field where a higher-definition liquid crystal display device is needed with downsizing of a pixel, a reduction in aperture ratio of a pixel (a proportion of an area of a light transmission part in a pixel), due to a wiring that forms a storage capacitor element (a storage capacitor wiring), needs to be suppressed. However, if the storage capacitor wiring is thinned to reduce the proportion of the area of the storage capacitor wiring in the pixel, a storage capacitance enough for high image qualities cannot be obtained. A technology of increasing the aperture ratio of the pixel with the storage capacitance being secured is now being needed. As such a technology, a technology of forming a storage capacitance using a structure in which an inter layer film, which is an insulating film in a pixel, is interposed between transparent conductive films is known (for example, refer to Patent Document 1).
MVA (multi-domain vertical alignment) mode, which is one kind of VA (vertical alignment) mode, is known as display mode excellent in viewing angle characteristics (for example, refer to Patent Document 2). In VA mode, negative anisotropic liquid crystal molecules are used, and the molecules are aligned vertically to substrate surfaces when no voltage (a voltage of less than a threshold value) is applied, and they are aligned horizontally to the substrate surfaces when a voltage (a voltage of a threshold value or more) is applied. In MVA mode, a structure for controlling alignment of liquid crystal molecules, such as a projective dielectric material (projection for liquid crystal alignment control) and an electrode slit, are formed on substrate surfaces in order to improve a response speed of the liquid crystal molecules at the time of voltage application and to increase a viewing angle.
In the MVA mode liquid crystal display device, as a technology of achieving both securement of a storage capacitance and increase in aperture ratio of a pixel, a technology of forming an auxiliary capacitance to overlap with a slit on a pixel electrode in the normal direction of an active matrix substrate, and a technology of overlapping an extending part of a storage capacitor wiring with a projection for liquid crystal alignment control and/or an electrode-free part are disclosed (for example, refer to Patent Documents 3 and 4). According to these technologies, a storage capacitor element, which is generally made of a shielding material, is arranged in a region where an alignment control structure is arranged, the region having less contribution as a light transmission region, and thereby both of the securement of the storage capacitance and the improvement in aperture ratio of the pixel are achieved.
In the MVA mode liquid crystal display device, it is known that light is leaked from a region where the projection for liquid crystal alignment control is arranged. For this problem, in Patent Document 1, a technology of shielding a part corresponding to the projection for liquid crystal alignment control with BM (black matrix) for improving a contrast ratio has been disclosed.
As mentioned above, the MVA mode liquid crystal display device needs to improve the contrast ratio by preventing light leaked from the region where the projection for liquid crystal alignment control is arranged, in addition to the securement of the storage capacitance and the improvement of the aperture ratio of the pixel. Therefore, the MVA mode liquid crystal display device still has room for improvement in that these problems are comprehensively solved.
[Patent Document 1]
    Japanese Kokai Publication No. Hei-08-43854[Patent Document 2]    Japanese Kokai Publication No. Hei-11-242225[Patent Document 3]    Japanese Kokai Publication No. 2006-154080[Patent Document 4]    WO 2006/54386